93 Corolla Head Unit Install

Hi I currently got a new head unit. After I finish putting my adapter harness together i ran into problem. What do i connect the ground to? To the harness or do i drill hole in body and ground it to the body metal?

What is a "head Unit"???? Diesel 1962

have you tried grounding it to the frame of the car. Where the radio is at the frame of the stereo is attached to the frame of the car if you cannot do this then ground the radio to itself worked for me!